Long-Term Evolution (“LTE”) is an effort to develop advanced wireless mobile radio technology that aims to succeed current Third Generation (“3G”) telecommunication standards and technology for mobile networking, including but not limited to Wideband Code Division Multiple Access (“WCDMA”), High-Speed Downlink Packet Access (“HSDPA”), and High-Speed Uplink Packet Access (“HSUPA”) technology. The actual standard is known as the International Telecommunication Union (“ITU”) 3rd Generation Partnership Project (“3GPP”), Release 8, although the term LTE is often used to reference the standard. LTE is considered by many to be a Fourth Generation (“4G”) technology, both because it is faster than 3G, and because, like the Internet, LTE uses an “all-IP” architecture where all information, including voice, is handled as data.
The LTE standard presently supports two modes of data allocation, localized and distributed. Localized transmission is intended for frequency selective scheduling, while distributed transmission is intended to maximize the amount of frequency diversity when sub-band channel knowledge is not available or out-of-date at the scheduler.
The minimum resource allocation size is called a Virtual Resource Block (“VRB”). Two types of VRBs, diversity VRB and localized VRB, are used to support the localized transmission and the distributed transmission. A Physical Resource Block (“PRB”) is a set of time frequency resources that is the same size as a VRB. The mapping of a VRB to a PRB is decided for localized transmission as a simple identity mapping, i.e., first VRB goes to first PRB, second VRB goes to second PRB, etc.
For a localized VRB assignment, two methods may be applied: a “compact” method and a “full” method. The compact method can only allocate consecutive VRB indices, and thus has limited flexibility. The full method assigns VRBs in one of two ways. First, consecutive VRBs may be grouped into groups of k which is equal to 1, 2, 3, or 4 consecutive Resource Blocks (“RBs”), where k depends on the bandwidth, and the RBs are assigned groups using a bitmap. Second, by using a bitmap where each bit represents every 2nd, 3rd, or 4th RB, depending on the bandwidth, and where an offset indicates the position of the first VRB.
The RB allocation scheme mentioned above is mainly for the localized transmission, as the resources in a localized transmission should be located in close proximity, e.g., contiguously clustered together, for ease in processing and to achieve frequency selective gains. However, for a distributed transmission, the end user devices do not care where the data is located, as long as it scattered across the channel. LTE does not distinguish between the two different types of transmissions and forces the wireless device to use the same mapping scheme for distributed transmission as for localized transmission. This requirement adds additional, unnecessary overhead to processing the distributed transmissions.
However, it is desirable to schedule the localized transmission and the distributed transmission simultaneously. Some diversity gain can be obtained using localized channel allocation by assigning single RBs scattered across the band. However, this practice only works when multiple RBs are assigned to a single device or User Equipment (“UE”). The above methods cannot provide sufficient diversity to small packet sizes. Additionally, the overhead required to schedule individual RB across the band is higher than assigning contiguous resources.
Therefore, what is needed is a system and method for mapping between distributed RB indices and physical RBs which allows for maximal commonality and/or coexistence with a localized transmission arrangement while still achieving good performance and low signaling overhead.